Carnot was primarily concerned with and the mechanical power which could be obtained from the fire heating upthe hot reservoir (the cold reservoir being provided from the surroundingsat "no cost", from a water stream or from atmospheric air). He thus defined the efficiency of an engine as the ratio of the work doneto the quantity of heat transferred . For Carnot's ideal engine, the above shows that this ratio boils down tothe following quantity, known as :
Within the uncertainties involved in the diffusion coefficients used for n-heptane and n-octane, the Sherwood Numbers are comparable for both materials. A dimensionless Frössling Number is computed which characterizes either heat or mass transfer rates for cylinders on a comparable basis. The calculated Frössling Numbers based on mass transfer measurements are in substantial agreement with Frössling Numbers calculated from the data of other workers in heat transfer.
Because of the low operating pressure andsmall length scale of this thruster, unique forms of mass transferanalysis such as non-continuum gas flow were modeled using the DirectSimulation Monte Carlo method.
Continuum fluid/thermal simulations usingCOMSOL Multiphysics have been applied to model heat and mass transfer inthe solid and liquid portions of the thruster.
In the present work, a two-dimensional numerical model of heat and mass transfer for the convective drying of ceramic porous system was developed. The governing system of fully coupled non-linear partial differential equations describing the process was derived from a mechanistic approach. A formulation including hygrothermal and moisture transport in soil was adopted as the basis for further development in this work. The calculation results for drying of a ceramic brick showed that the model presented is in good agreement with other studies that have been reported previously in the drying of porous material. Further investigation on the shell drying agrees well with the most drying mechanism of ceramic porous body. The influence of material parameter on the drying profile is taken into consideration by carrying out some investigation on the material sensitivity study.
A heat pump is driven like a refrigeration unit,but its useful output is the heat transferred to the hot side(to make it warmer). A little heat comes from the electrical power not converted intomechanical work, the rest is "pumped" at an efficiency which always exceeds(by far) 100% of the mechanical work. For a Carnot engine, this latterefficiency is:
The primary purpose of a refrigerator (or an air-conditioning unit)is to extract heat from the cold source(to make it cooler). Its efficiency is thus usefully defined as theratio of that heat to the mechanical power used to produce the transfer. So defined, the efficiency of a Carnot engine driven (backwards) as a refrigerator is:
AB - Direct numerical simulation is used to assess the importance of compressibility in turbulent channel flow of a mixture of air and water vapor with dispersed water droplets. The dispersed phase is allowed to undergo phase transition, which leadsto heat and mass transfer between the phases. We compare simulation results obtainedwith an incompressible formulation with those obtained for compressible flow at various low values of Mach number. Results for flow properties obtained with the compressible model converge quickly to the incompressible results in case the Mach number is reduced. In contrast, thermal properties such as the Nusselt number, display a systematic difference between the two formulations on the order of 15%, even in the low-Mach limit. Second, a new efficient numerical algorithm for droplet-laden turbulent channel flow at low Mach numbers is proposed. In order to avoid very small time steps at low Mach numbers that would arise from stability requirements associated with explicit time-stepping we propose a new semi-explicit time integration method. We perform a perturbation analysis in powers of the Mach number of the system of governing equations. An important feature of the new numerical approach is the independence of the maximum allowed time step on the Mach number. We validate the new method by comparing it with a fully explicit code for compressible flow at general Mach numbers showing a good agreement in all quantities of interest. Finally, we consider turbulent droplet-laden channel flow with phase transition in the presence of gravity in the wall-normal direction and a thin film of water at the bottom wall. We maintain the film thickness constant by draining water from the bottom wall to compensate for (a) the droplets that fall onto the film and (b) evaporation/condensation. We also maintain on average the total mass of water in the channel by inserting new droplets at the top wall to compensate for the water that has been drained from the bottom wall. We analyze the behavior of the statistically averaged gas and droplet quantities focusing on the heat exchange between the two phases.
Ilic, M., and Turner, I. W., Convective drying of a consolidated slab of wet porous material, International Journal of Heat and Mass Transfer, 1989, 32, 2351–2362.
Could itself be the extensive quantity involved in the energybalance of an infinitesimal energy balance for an irreversible transformation? The answer is a resounding . This misguided explanation would essentially be equivalent toconsidering heat as some kind of conserved fluid (formerly dubbed "caloric"). The naive was first shown to be untenableby in 1798.
Gross Sherwood Numbers are calculated from the data and are in substantial agreement with existing correlations of the results of other workers. The Sherwood Numbers, characterizing mass transfer rates, increase approximately as the 0.55 power of theReynolds Number. At a free stream Reynolds Number of 3700 theSherwood Number showed a 40% increase as the apparent turbulence level of the free stream was raised from 1.3 to 25 per cent.